Automatic transmissions typically will use a torque reduction of the engine when performing an upshift. An upshift is when the transmission shifts from a gear with a higher numerical multiplication ratio to a lower numerical multiplication ratio, such as a shift from second gear to third gear. When this is done, the engine speed must slow down to provide a speed that corresponds with the transmission output speed multiplied by the transmission gear block ratio. To slow down the engine faster without wearing the transmission clutch material excessively or providing an acceleration to the driver, the engine torque is decreased quickly and then brought back up to a torque corresponding with the transmission output torque.
The airflow torque (i.e., engine torque affected by the throttle, a turbobooster system and/or a supercharger system, and valve phasers) during an automatic transmission upshift will typically increase during the shift because it takes a higher engine torque to make the same axle torque with a lower numerical ratio gear. There is typically a delay between requesting an airflow torque and achieving it.
In known systems, during an upshift, the transmission control module will usually issue an immediate torque reduction request that is satisfied with spark retard. The spark retard takes energy out of the combustion event and puts it into the exhaust system as heat. The immediate torque request brings down the engine torque to be able to aid in bringing down the engine speed during the shift. Toward the end of the shift, the immediate torque request will start ramping up again (i.e., request a higher torque value) to give torque back to the normal driver control path (based on the airflow request and sent from the engine controller to the transmission controller) with optimal efficiency.